Complex REE zonations in metamorphic garnet reflect accessory mineral reactions

Abstract

A garnet from the Sesia Zone, NW Italy, was selected for Major and Rare Earth Element (REE) mapping, using LA-ICP-MS – a procedure previously not conducted at the Department of Earth Science at University of Gothenburg. The original inclusion assemblage of the garnet is preserved, and the mapping revealed two distinct changes in both garnet chemistry and inclusion assemblage, both which can be linked to the metamorphic development of the region. The onset and disappearance of REE bearing inclusions is mirrored in the garnet, as it showed fluctuating concentrations of REEs, while the mineral assemblage changed. The REEs are in this case the most valuable tool we have in terms of interpreting relict mineral reactions. If researched enough, the REEs on their own might yield enough information to interpret metamorphic events such as subduction episodes. Key words: RARE EARTH ELEMENTS, REEs, GARNET, METAMORPHISM